GLIMR: A GIS-BASED METHOD FOR THE GEOMETRIC MORPHOMETRIC ANALYSIS OF ARTIFACTS

Abstract

Archaeology's participation in the digital renaissance of the twenty-first century requires adequate operationalization of technological methods, such as three-dimensional scanning. Here, we describe and demonstrate a geographic information systems-based lithic morphometric research (GLiMR) software approach. GLiMR accurately and rapidly handles a sequence of ArcGIS procedures to extract geometric morphometric data from 2D and 3D scan files that are impractical to record by hand, opening new doors to the analysis of lithic artifacts. GLiMR generates three main types of geometric properties: shape data, topographic data, and domain aggregate data. These data can be extracted in ways that support other analyses of artifact form, including generalized Procrustes analysis, principal components analysis, and cluster analyses. We illustrate the use of GLiMR by presenting a basic case study that compares the geometric morphometry of Western Stemmed Tradition projectile points found in two cache features at Idaho's Cooper's Ferry site and from other sites in the Columbia River Plateau region of the Pacific Northwest. Cluster analyses of the generalized Procrustes analysis of 3D landmarks from Cooper's Ferry cache points fail to separate the two caches from one another on the basis of their geometric morphometric attributes. We interpret these results to suggest that these stemmed projectile points were probably created by persons who shared a specific set of technological production guidelines for the manufacture of Western Stemmed Tradition projectile points. Cluster analyses indicate that Cooper's Ferry Western Stemmed Tradition projectile points can be morphometrically separated from stemmed points found at other regional sites; however, significant overlaps were seen among stemmed projectile points from the Pilcher Creek site, which may suggest the existence of contemporaneous information sharing networks or macroband territorial movements.

Keywords:

• Geometric morphometry
• Geographic information systems
• Western Stemmed Tradition
• Three dimensional scanning

Notes

1 The GLiMR toolset, instruction manual, and 3D data used in this analysis are available at: http://hdl.handle.net/1957/55540. The associated DOI is: 10.7267/N9NP22CF.

2 We have found that collecting single face scans is more efficient than creating a single closed 3D model. Creating a closed watertight model manually is very time consuming. The same geometry information can be extracted by using two single face point clouds that meet exactly on a shared bifacial margin. The proposed method is capable of programmatically aligning two single face scans in 3D space which can be used to examine degrees of bifacial symmetry, edge angles, or thickness.

3 MeshLab can be downloaded at: http://meshlab.sourceforge.net/. MeshLab is used to separate closed 360° models into two distinct scans for subsequent GLiMR analysis.

4 Prior to 3D scanning, we prepared the artifact surfaces with talc to increase material opacity and reduce reflectiveness during laser scanning. NextEngine 3D scans were created at the machine's highest resolution of 40,000 data points per square inch (40,000 data points per 6.45 cm²). Due to their particular geometry, some artifacts required more individual scans to get complete coverage of their form (e.g., 3–12 scans per artifact side; 6–24 scans for 360° coverage). Because of this, total elapsed time to create a 3D model of a single artifact face varied from 2 to 8 hours. Typically, scans were captured with a biface positioned in a vertical orientation with one face normal to the NextEngine laser. Afterwards, a series of oblique angle scans were taken to obtain complete coverage. Single face scans are saved in .xyz format, typically contain between 10,000 and 30,000 points and are around 1–3 MB in size. We used a Microsoft Windows 7 computer with an Intel i7 with 16 GB of RAM and an ATI Radeon 6670 videocard. The geodatabase containing all geometry and derived attributes of an individual artifact ranges between 50 and 100 MB in size; however, a summary-only database is produced that is approximately 300 KB per face. Procrustes landmark data are exported by GLiMR in the .TPS file format.

Additional information

Notes on contributors

Loren G. Davis

Loren G. Davis is an Associate Professor of Anthropology at Oregon State University where he serves as the Executive Director of the Keystone Archaeological Research Fund and Directs the Pacific Slope Archaeological Laboratory. Davis specializes in the archaeology and geoarchaeology of the Pacific Northwest and the Baja California peninsula. He is particularly interested in archaeological methodologies and the application of digital technologies to the solution of analytical problems. Notable recent publications include a co-editorship and authorship in Trekking the Shore.

Correspondence to: Loren G. Davis, Pacific Slope Archaeological Laboratory, Oregon State University, Department of Anthropology, 238 Waldo Hall, Corvallis, OR 97331, USA. Email: [email protected]

Daniel W. Bean

Daniel Bean is a retired geologist with interests in stratigraphy, depositional processes, geographic information systems, programming, data structures and descriptive geometry. Recent collaboration with Davis and Nyers has allowed cross-discipline techniques to be developed related to geometric morphometrics of lithic artifacts.

Alex J. Nyers

Alex Nyers works as a Faculty Research Assistant at the Pacific Slope Archaeological Laboratory. His interests are centered on leveraging emerging technologies to gain new insights into complex archaeological problems. Mr. Nyers is the project lead for “Archie”, an open source archaeological inventory system. He has experience with 3D scanning and printing technologies, morphometric analyses, and provenance studies centered in crypto-crystalline silicates.

David R. Brauner

David R. Brauner has served as professor of anthropology at OSU since 1977, with a research focus on historical archeology of the Pacific Northwest. With his students, Brauner has researched topics including the French-Canadian/Métis employees of the Hudson's Bay Company (Oregon's first non-native settlers), and the role of the military and its forts in Oregon during and after the American Civil War. He also directed excavations at the Alpowai Village site and the Pilcher Creek sites—key projects that inform our understanding of southern Columbia River Plateau prehistory.